硫酸盐侵蚀掺水泥级配碎石膨胀时变机理研究

Cement stabilized graded macadam is widely used in high-speed railway subgrade transition section. When Cement stabilized graded macadam is attacked by sulfate, it has caused serious expansion diseases on high speed railway. At present, the study on expansion mechanism of sulfate attack on cement stabilized soil is mainly focused on the fine granular soil . This project mainly focuses on the research of time-dependent expansion mechanism of sulfate attack on cement stabilized graded macadam. Systematically study will be carried out on the micro mechanism of sulfate erosion expansion process through X-CT test, XRD, NMR and 3D reconstruction technique, from the perspective of the interaction between coarse particle skeleton with expansion material and salt migration absorption . The mineral activity state and potential expansion potential of the Cement stabilized graded macadam will be studied through mineral analysis technology. Laboratory tests will be conducted for time-dependent expansion developing trend of sulfate attack on cement stabilized graded macadam , suggest the critical conditions of the proposed expansion. The expansion deformation model will be established and put forward the prediction method of expansion deformation. The research will give guidance to predict the expansion trend of existing fillers and the selection of new high speed railway fillers ，the theory of sulfate attack on cement stabilized graded macadam expansion characteristics has important theoretical and practical significance.

掺水泥级配碎石广泛应用于高速铁路路基过渡段，硫酸盐侵蚀条件下将引起膨胀变形病害。目前硫酸盐侵蚀水泥改良土膨胀的研究主要集中在细颗粒土方面，缺少针对掺水泥级配碎石的研究，尚未掌握硫酸盐侵蚀掺水泥级配碎石膨胀变形规律及时变机理。在国内外学者研究工作的基础上，本项目采用矿物分析技术研究掺水泥级配碎石矿物活性状态及潜在膨胀势的刻画方法，通过X-CT微观扫描、三维重构及数值模拟，阐述钙矾石晶体与粗颗粒骨架之间填充、挤胀的作用关系，基于膨胀过程中掺水泥级配碎石填料渗透特性的变化特点，研究硫酸盐侵蚀过程微观膨胀机理以及填料宏观膨胀变形规律，明确掺水泥级配碎石膨胀发展的关键性制约指标，建立掺水泥级配碎石膨胀变形时效模型，提出膨胀变形预测方法。深入认识该类填料侵蚀膨胀时变特性，对预测膨胀变形发展趋势及做出合理判断，具有重大的理论和实践意义。

随着我国高速铁路运营里程的增加，路网覆盖范围的增大，多条无砟轨道线路出现了路基上拱变形病害，严重影响了高铁的正常运营秩序，硫酸盐侵蚀掺水泥级配碎石膨胀是其中典型的形式之一。本课题通过现场调研、室内试验、理论分析等手段对硫酸盐侵蚀掺水泥级配碎石膨胀时变机理研究开展研究，主要结论如下：.（1）揭示了硫酸盐侵蚀膨胀活性矿物细观形貌与分布状态特征。针对硫酸盐侵蚀膨胀钙矾石、硅灰石膏等典型矿物开展了电子显微镜、X-CT断层扫描试验，揭示了活性矿物细观形貌特征，系统查明了各类矿物晶体成分含量。.（2）提出了硫酸盐侵蚀掺水泥填料细观膨胀机理。掺水泥填料呈碱性，极大提升了惰性原土料的的化学活性，导致硫酸盐与水泥以及土体中硅酸盐、碳酸盐矿物发生化学反应形成钙矾石、硅灰石膏晶体，形成过程中以化学反应的形式吸收水和盐分，晶体体积增大。多个晶体以簇状形式在颗粒表面堆积，形成具有一定孔隙的簇状体，较高的结晶压力下晶体交叉生长而相互推斥使得土颗粒间的孔隙不断增大，导致掺水泥填料体积膨胀。.（3）明晰了硫酸盐侵蚀掺水泥填料膨胀过程。受水盐迁移以及地温变化影响，硫酸盐侵蚀掺水泥填料具有寒季变形较快，夏季变形较慢的季节性变形规律，膨胀变形主要发生在地温较低的寒季当中，且具有不可逆性，导致硫酸盐侵蚀膨胀发生长达数年的持续膨胀变形。.（4）提出了掺水泥填料膨胀时变模型。根据硫酸盐侵蚀膨胀离子析出—化学反应—晶体沉淀—离子迁移膨胀多过程作用，建立了硫酸盐侵蚀膨胀时变模型，通过化学反应速率公式表述整个硫酸盐侵蚀膨胀过程。